File: rfc2759.txt

package info (click to toggle)
doc-rfc 20181229-2
  • links: PTS, VCS
  • area: non-free
  • in suites: buster
  • size: 570,944 kB
  • sloc: xml: 285,646; sh: 107; python: 90; perl: 42; makefile: 14
file content (1123 lines) | stat: -rw-r--r-- 34,178 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123






Network Working Group                                            G. Zorn
Request for Comments: 2759                         Microsoft Corporation
Category: Informational                                     January 2000


                Microsoft PPP CHAP Extensions, Version 2


Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.  PPP
   defines an extensible Link Control Protocol and a family of Network
   Control Protocols (NCPs) for establishing and configuring different
   network-layer protocols.

   This document describes version two of Microsoft's PPP CHAP dialect
   (MS-CHAP-V2).  MS-CHAP-V2 is similar to, but incompatible with, MS-
   CHAP version one (MS-CHAP-V1, described in [9]).  In particular,
   certain protocol fields have been deleted or reused but with
   different semantics.  In addition, MS-CHAP-V2 features mutual
   authentication.

   The algorithms used in the generation of various MS-CHAP-V2 protocol
   fields are described in section 8.  Negotiation and hash generation
   examples are provided in section 9.

Specification of Requirements

   In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
   "recommended", "SHOULD", and "SHOULD NOT" are to be interpreted as
   described in [3].









Zorn                         Informational                      [Page 1]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. LCP Configuration . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Challenge Packet  . . . . . . . . . . . . . . . . . . . . . . .  3
   4. Response Packet . . . . . . . . . . . . . . . . . . . . . . . .  4
   5. Success Packet  . . . . . . . . . . . . . . . . . . . . . . . .  4
   6. Failure Packet  . . . . . . . . . . . . . . . . . . . . . . . .  5
   7. Change-Password Packet  . . . . . . . . . . . . . . . . . . . .  6
   8. Pseudocode  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   8.1. GenerateNTResponse()  . . . . . . . . . . . . . . . . . . . .  7
   8.2. ChallengeHash() . . . . . . . . . . . . . . . . . . . . . . .  8
   8.3. NtPasswordHash()  . . . . . . . . . . . . . . . . . . . . . .  9
   8.4. HashNtPasswordHash()  . . . . . . . . . . . . . . . . . . . .  9
   8.5. ChallengeResponse() . . . . . . . . . . . . . . . . . . . . .  9
   8.6. DesEncrypt()  . . . . . . . . . . . . . . . . . . . . . . . . 10
   8.7. GenerateAuthenticatorResponse() . . . . . . . . . . . . . . . 10
   8.8. CheckAuthenticatorResponse()  . . . . . . . . . . . . . . . . 12
   8.9. NewPasswordEncryptedWithOldNtPasswordHash() . . . . . . . . . 12
   8.10. EncryptPwBlockWithPasswordHash() . . . . . . . . . . . . . . 13
   8.11. Rc4Encrypt() . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.12. OldNtPasswordHashEncryptedWithNewNtPasswordHash()  . . . . . 14
   8.13. NtPasswordHashEncryptedWithBlock() . . . . . . . . . . . . . 14
   9. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   9.1. Negotiation Examples  . . . . . . . . . . . . . . . . . . . . 14
   9.1.1. Successful authentication . . . . . . . . . . . . . . . . . 15
   9.1.2. Authenticator authentication failure  . . . . . . . . . . . 15
   9.1.3. Failed authentication with no retry allowed . . . . . . . . 15
   9.1.4. Successful authentication after retry . . . . . . . . . . . 15
   9.1.5. Failed hack attack with 3 attempts allowed  . . . . . . . . 15
   9.1.6. Successful authentication with password change  . . . . . . 16
   9.1.7. Successful authentication with retry and password change. . 16
   9.2. Hash Example  . . . . . . . . . . . . . . . . . . . . . . . . 16
   9.3. Example of DES Key Generation . . . . . . . . . . . . . . . . 17
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
   14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 20












Zorn                         Informational                      [Page 2]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


1.  Introduction

   Where possible, MS-CHAP-V2 is consistent with both MS-CHAP-V1 and
   standard CHAP.  Briefly, the differences between MS-CHAP-V2 and MS-
   CHAP-V1 are:

   *  MS-CHAP-V2 is enabled by negotiating CHAP Algorithm 0x81 in LCP
      option 3, Authentication Protocol.

   *  MS-CHAP-V2 provides mutual authentication between peers by
      piggybacking a peer challenge on the Response packet and an
      authenticator response on the Success packet.

   *  The calculation of the "Windows NT compatible challenge response"
      sub-field in the Response packet has been changed to include the
      peer challenge and the user name.

   *  In MS-CHAP-V1, the "LAN Manager compatible challenge response"
      sub-field was always sent in the Response packet.  This field has
      been replaced in MS-CHAP-V2 by the Peer-Challenge field.

   *  The format of the Message field in the Failure packet has been
      changed.

   *  The Change Password (version 1) and Change Password (version 2)
      packets are no longer supported. They have been replaced with a
      single Change-Password packet.

2.  LCP Configuration

   The LCP configuration for MS-CHAP-V2 is identical to that for
   standard CHAP, except that the Algorithm field has value 0x81, rather
   than the MD5 value 0x05.  PPP implementations which do not support
   MS-CHAP-V2, but correctly implement LCP Config-Rej, should have no
   problem dealing with this non-standard option.

3.  Challenge Packet

   The MS-CHAP-V2 Challenge packet is identical in format to the
   standard CHAP Challenge packet.

   MS-CHAP-V2 authenticators send an 16-octet challenge Value field.
   Peers need not duplicate Microsoft's algorithm for selecting the 16-
   octet value, but the standard guidelines on randomness [1,2,7] SHOULD
   be observed.

   Microsoft authenticators do not currently provide information in the
   Name field.  This may change in the future.



Zorn                         Informational                      [Page 3]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


4.  Response Packet

   The MS-CHAP-V2 Response packet is identical in format to the standard
   CHAP Response packet.  However, the Value field is sub-formatted
   differently as follows:

   16 octets: Peer-Challenge
    8 octets: Reserved, must be zero
   24 octets: NT-Response
    1 octet : Flags

   The Peer-Challenge field is a 16-octet random number.  As the name
   implies, it is generated by the peer and is used in the calculation
   of the NT-Response field, below.  Peers need not duplicate
   Microsoft's algorithm for selecting the 16-octet value, but the
   standard guidelines on randomness [1,2,7] SHOULD be observed.

   The NT-Response field is an encoded function of the password, the
   user name, the contents of the Peer-Challenge field and the received
   challenge as output by the routine GenerateNTResponse() (see section
   8.1, below).  The Windows NT password is a string of 0 to
   (theoretically) 256 case-sensitive Unicode [8] characters.  Current
   versions of Windows NT limit passwords to 14 characters, mainly for
   compatibility reasons; this may change in the future.  When computing
   the NT-Response field contents, only the user name is used, without
   any associated Windows NT domain name.  This is true regardless of
   whether a Windows NT domain name is present in the Name field (see
   below).

   The Flag field is reserved for future use and MUST be zero.

   The Name field is a string of 0 to (theoretically) 256 case-sensitive
   ASCII characters which identifies the peer's user account name.  The
   Windows NT domain name may prefix the user's account name (e.g.
   "BIGCO\johndoe" where "BIGCO" is a Windows NT domain containing the
   user account "johndoe").  If a domain is not provided, the backslash
   should also be omitted, (e.g. "johndoe").

5.  Success Packet

   The Success packet is identical in format to the standard CHAP
   Success packet.  However, the Message field contains a 42-octet
   authenticator response string and a printable message.  The format of
   the message field is illustrated below.

   "S=<auth_string> M=<message>"





Zorn                         Informational                      [Page 4]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


   The <auth_string> quantity is a 20 octet number encoded in ASCII as
   40 hexadecimal digits.  The hexadecimal digits A-F (if present) MUST
   be uppercase.  This number is derived from the challenge from the
   Challenge packet, the Peer-Challenge and NT-Response fields from the
   Response packet, and the peer password as output by the routine
   GenerateAuthenticatorResponse() (see section 8.7, below).  The
   authenticating peer MUST verify the authenticator response when a
   Success packet is received.  The method for verifying the
   authenticator is described in section 8.8, below.  If the
   authenticator response is either missing or incorrect, the peer MUST
   end the session.

   The <message> quantity is human-readable text in the appropriate
   charset and language [12].

6.  Failure Packet

   The Failure packet is identical in format to the standard CHAP
   Failure packet.  There is, however, formatted text stored in the
   Message field which, contrary to the standard CHAP rules, does affect
   the operation of the protocol.  The Message field format is:

      "E=eeeeeeeeee R=r C=cccccccccccccccccccccccccccccccc V=vvvvvvvvvv
M=<msg>"

      where

      The "eeeeeeeeee" is the ASCII representation of a decimal error
      code (need not be 10 digits) corresponding to one of those listed
      below, though implementations should deal with codes not on this
      list gracefully.

         646 ERROR_RESTRICTED_LOGON_HOURS
         647 ERROR_ACCT_DISABLED
         648 ERROR_PASSWD_EXPIRED
         649 ERROR_NO_DIALIN_PERMISSION
         691 ERROR_AUTHENTICATION_FAILURE
         709 ERROR_CHANGING_PASSWORD

      The "r" is an ASCII flag set to '1' if a retry is allowed, and '0'
      if not.  When the authenticator sets this flag to '1' it disables
      short timeouts, expecting the peer to prompt the user for new
      credentials and resubmit the response.

      The "cccccccccccccccccccccccccccccccc" is the ASCII representation
      of a hexadecimal challenge value.  This field MUST be exactly 32
      octets long and MUST be present.




Zorn                         Informational                      [Page 5]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


      The "vvvvvvvvvv" is the ASCII representation of a decimal version
      code (need not be 10 digits) indicating the password changing
      protocol version supported on the server.  For MS-CHAP-V2, this
      value SHOULD always be 3.

      <msg> is human-readable text in the appropriate charset and
      language [12].

7.  Change-Password Packet

   The Change-Password packet does not appear in either standard CHAP or
   MS-CHAP-V1.  It allows the peer to change the password on the account
   specified in the preceding Response packet.  The Change-Password
   packet should be sent only if the authenticator reports
   ERROR_PASSWD_EXPIRED (E=648) in the Message field of the Failure
   packet.

   This packet type is supported by recent versions of Windows NT 4.0,
   Windows 95 and Windows 98.  It is not supported by Windows NT 3.5,
   Windows NT 3.51, or early versions of Windows NT 4.0, Windows 95 and
   Windows 98.

   The format of this packet is as follows:

        1 octet  : Code
        1 octet  : Identifier
        2 octets : Length
      516 octets : Encrypted-Password
       16 octets : Encrypted-Hash
       16 octets : Peer-Challenge
        8 octets : Reserved
       24 octets : NT-Response
        2-octet  : Flags

   Code
      7

   Identifier
      The Identifier field is one octet and aids in matching requests
      and replies.  The value is the Identifier of the received Failure
      packet to which this packet responds plus 1.

   Length
      586







Zorn                         Informational                      [Page 6]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


   Encrypted-Password
      This field contains the PWBLOCK form of the new Windows NT
      password encrypted with the old Windows NT password hash, as
      output by the NewPasswordEncryptedWithOldNtPasswordHash() routine
      (see section 8.9, below).

   Encrypted-Hash
      This field contains the old Windows NT password hash encrypted
      with the new Windows NT password hash, as output by the
      OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine (see
      section 8.12, below).

   Peer-Challenge
      A 16-octet random quantity, as described in the Response packet
      description.

   Reserved
      8 octets, must be zero.

   NT-Response
      The NT-Response field (as described in the Response packet
      description), but calculated on the new password and the challenge
      received in the Failure packet.

   Flags
      This field is two octets in length.  It is a bit field of option
      flags where 0 is the least significant bit of the 16-bit quantity.
      The format of this field is illustrated in the following diagram:

                    1
          5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                               |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Bits 0-15
            Reserved, always clear (0).

8.  Pseudocode

   The routines mentioned in the text above are described in pseudocode
   in the following sections.

8.1.  GenerateNTResponse()

   GenerateNTResponse(
   IN  16-octet              AuthenticatorChallenge,
   IN  16-octet              PeerChallenge,



Zorn                         Informational                      [Page 7]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


   IN  0-to-256-char         UserName,

   IN  0-to-256-unicode-char Password,
   OUT 24-octet              Response )
   {
      8-octet  Challenge
      16-octet PasswordHash

      ChallengeHash( PeerChallenge, AuthenticatorChallenge, UserName,
                     giving Challenge)

      NtPasswordHash( Password, giving PasswordHash )
      ChallengeResponse( Challenge, PasswordHash, giving Response )
   }

8.2.  ChallengeHash()

   ChallengeHash(
   IN 16-octet               PeerChallenge,
   IN 16-octet               AuthenticatorChallenge,
   IN  0-to-256-char         UserName,
   OUT 8-octet               Challenge
   {

      /*
       * SHAInit(), SHAUpdate() and SHAFinal() functions are an
       * implementation of Secure Hash Algorithm (SHA-1) [11]. These are
       * available in public domain or can be licensed from
       * RSA Data Security, Inc.
       */

      SHAInit(Context)
      SHAUpdate(Context, PeerChallenge, 16)
      SHAUpdate(Context, AuthenticatorChallenge, 16)

      /*
       * Only the user name (as presented by the peer and
       * excluding any prepended domain name)
       * is used as input to SHAUpdate().
       */

      SHAUpdate(Context, UserName, strlen(Username))
      SHAFinal(Context, Digest)
      memcpy(Challenge, Digest, 8)
   }






Zorn                         Informational                      [Page 8]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


8.3.  NtPasswordHash()

   NtPasswordHash(
   IN  0-to-256-unicode-char Password,
   OUT 16-octet              PasswordHash )
   {
      /*
       * Use the MD4 algorithm [5] to irreversibly hash Password
       * into PasswordHash.  Only the password is hashed without
       * including any terminating 0.
       */
   }

8.4.  HashNtPasswordHash()

   HashNtPasswordHash(
   IN  16-octet PasswordHash,
   OUT 16-octet PasswordHashHash )
   {
      /*
       * Use the MD4 algorithm [5] to irreversibly hash
       * PasswordHash into PasswordHashHash.
       */
   }

8.5.  ChallengeResponse()

   ChallengeResponse(
   IN  8-octet  Challenge,
   IN  16-octet PasswordHash,
   OUT 24-octet Response )
   {
      Set ZPasswordHash to PasswordHash zero-padded to 21 octets

      DesEncrypt( Challenge,
                  1st 7-octets of ZPasswordHash,
                  giving 1st 8-octets of Response )

      DesEncrypt( Challenge,
                  2nd 7-octets of ZPasswordHash,
                  giving 2nd 8-octets of Response )

      DesEncrypt( Challenge,
                  3rd 7-octets of ZPasswordHash,
                  giving 3rd 8-octets of Response )
   }





Zorn                         Informational                      [Page 9]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


8.6.  DesEncrypt()

   DesEncrypt(
   IN  8-octet Clear,
   IN  7-octet Key,
   OUT 8-octet Cypher )
   {
      /*
       * Use the DES encryption algorithm [4] in ECB mode [10]
       * to encrypt Clear into Cypher such that Cypher can
       * only be decrypted back to Clear by providing Key.
       * Note that the DES algorithm takes as input a 64-bit
       * stream where the 8th, 16th, 24th, etc.  bits are
       * parity bits ignored by the encrypting algorithm.
       * Unless you write your own DES to accept 56-bit input
       * without parity, you will need to insert the parity bits
       * yourself.
       */
   }

8.7.  GenerateAuthenticatorResponse()

   GenerateAuthenticatorResponse(
   IN  0-to-256-unicode-char Password,
   IN  24-octet              NT-Response,
   IN  16-octet              PeerChallenge,
   IN  16-octet              AuthenticatorChallenge,
   IN  0-to-256-char         UserName,
   OUT 42-octet              AuthenticatorResponse )
   {
      16-octet              PasswordHash
      16-octet              PasswordHashHash
      8-octet               Challenge

      /*
       * "Magic" constants used in response generation
       */

      Magic1[39] =
         {0x4D, 0x61, 0x67, 0x69, 0x63, 0x20, 0x73, 0x65, 0x72, 0x76,
          0x65, 0x72, 0x20, 0x74, 0x6F, 0x20, 0x63, 0x6C, 0x69, 0x65,
          0x6E, 0x74, 0x20, 0x73, 0x69, 0x67, 0x6E, 0x69, 0x6E, 0x67,
          0x20, 0x63, 0x6F, 0x6E, 0x73, 0x74, 0x61, 0x6E, 0x74};








Zorn                         Informational                     [Page 10]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


      Magic2[41] =
         {0x50, 0x61, 0x64, 0x20, 0x74, 0x6F, 0x20, 0x6D, 0x61, 0x6B,
          0x65, 0x20, 0x69, 0x74, 0x20, 0x64, 0x6F, 0x20, 0x6D, 0x6F,
          0x72, 0x65, 0x20, 0x74, 0x68, 0x61, 0x6E, 0x20, 0x6F, 0x6E,
          0x65, 0x20, 0x69, 0x74, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6F,
          0x6E};

      /*
       * Hash the password with MD4
       */

      NtPasswordHash( Password, giving PasswordHash )

      /*
       * Now hash the hash
       */

      HashNtPasswordHash( PasswordHash, giving PasswordHashHash)

      SHAInit(Context)
      SHAUpdate(Context, PasswordHashHash, 16)
      SHAUpdate(Context, NTResponse, 24)
      SHAUpdate(Context, Magic1, 39)
      SHAFinal(Context, Digest)

      ChallengeHash( PeerChallenge, AuthenticatorChallenge, UserName,
                     giving Challenge)

      SHAInit(Context)
      SHAUpdate(Context, Digest, 20)
      SHAUpdate(Context, Challenge, 8)
      SHAUpdate(Context, Magic2, 41)
      SHAFinal(Context, Digest)

      /*
       * Encode the value of 'Digest' as "S=" followed by
       * 40 ASCII hexadecimal digits and return it in
       * AuthenticatorResponse.
       * For example,
       *   "S=0123456789ABCDEF0123456789ABCDEF01234567"
       */

   }








Zorn                         Informational                     [Page 11]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


8.8.  CheckAuthenticatorResponse()

   CheckAuthenticatorResponse(
   IN  0-to-256-unicode-char Password,
   IN  24-octet              NtResponse,
   IN  16-octet              PeerChallenge,
   IN  16-octet              AuthenticatorChallenge,
   IN  0-to-256-char         UserName,
   IN  42-octet              ReceivedResponse,
   OUT Boolean               ResponseOK )
   {

      20-octet MyResponse

      set ResponseOK = FALSE
      GenerateAuthenticatorResponse( Password, NtResponse, PeerChallenge,
                                     AuthenticatorChallenge, UserName,
                                     giving MyResponse)

      if (MyResponse = ReceivedResponse) then set ResponseOK = TRUE
      return ResponseOK
   }

8.9.  NewPasswordEncryptedWithOldNtPasswordHash()

   datatype-PWBLOCK
   {
      256-unicode-char Password
      4-octets         PasswordLength
   }

   NewPasswordEncryptedWithOldNtPasswordHash(
   IN  0-to-256-unicode-char NewPassword,
   IN  0-to-256-unicode-char OldPassword,
   OUT datatype-PWBLOCK      EncryptedPwBlock )
   {
      NtPasswordHash( OldPassword, giving PasswordHash )

      EncryptPwBlockWithPasswordHash( NewPassword,
                                      PasswordHash,
                                      giving EncryptedPwBlock )
   }









Zorn                         Informational                     [Page 12]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


8.10.  EncryptPwBlockWithPasswordHash()

   EncryptPwBlockWithPasswordHash(
   IN  0-to-256-unicode-char Password,
   IN  16-octet              PasswordHash,
   OUT datatype-PWBLOCK      PwBlock )
   {

      Fill ClearPwBlock with random octet values

         PwSize = lstrlenW( Password ) * sizeof( unicode-char )
         PwOffset = sizeof( ClearPwBlock.Password ) - PwSize
         Move PwSize octets to (ClearPwBlock.Password + PwOffset ) from
   Password
         ClearPwBlock.PasswordLength = PwSize
         Rc4Encrypt( ClearPwBlock,
                     sizeof( ClearPwBlock ),
                     PasswordHash,
                     sizeof( PasswordHash ),
                     giving PwBlock )
      }

8.11.  Rc4Encrypt()

   Rc4Encrypt(
   IN  x-octet Clear,
   IN  integer ClearLength,
   IN  y-octet Key,
   IN  integer KeyLength,
   OUT x-octet Cypher )
   {
      /*
       * Use the RC4 encryption algorithm [6] to encrypt Clear of
       * length ClearLength octets into a Cypher of the same length
       * such that the Cypher can only be decrypted back to Clear
       * by providing a Key of length KeyLength octets.
       */
   }













Zorn                         Informational                     [Page 13]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


8.12.  OldNtPasswordHashEncryptedWithNewNtPasswordHash()

   OldNtPasswordHashEncryptedWithNewNtPasswordHash(
   IN  0-to-256-unicode-char NewPassword,
   IN  0-to-256-unicode-char OldPassword,
   OUT 16-octet              EncryptedPasswordHash )
   {
      NtPasswordHash( OldPassword, giving OldPasswordHash )
      NtPasswordHash( NewPassword, giving NewPasswordHash )
      NtPasswordHashEncryptedWithBlock( OldPasswordHash,
                                        NewPasswordHash,
                                        giving EncryptedPasswordHash )
   }

8.13.  NtPasswordHashEncryptedWithBlock()

   NtPasswordHashEncryptedWithBlock(
   IN  16-octet PasswordHash,
   IN  16-octet Block,
   OUT 16-octet Cypher )
   {
      DesEncrypt( 1st 8-octets PasswordHash,
                  1st 7-octets Block,
                  giving 1st 8-octets Cypher )

      DesEncrypt( 2nd 8-octets PasswordHash,
                  2nd 7-octets Block,
                  giving 2nd 8-octets Cypher )
   }

9.  Examples

   The following sections include protocol negotiation and hash
   generation examples.

9.1.  Negotiation Examples

   Here are some examples of typical negotiations.  The peer is on the
   left and the authenticator is on the right.

   The packet sequence ID is incremented on each authentication retry
   response and on the change password response.  All cases where the
   packet sequence ID is updated are noted below.

   Response retry is never allowed after Change Password.  Change
   Password may occur after response retry.





Zorn                         Informational                     [Page 14]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


9.1.1.  Successful authentication

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Success/Authenticator Response

   (Authenticator Response verification succeeds, call continues)

9.1.2.  Authenticator authentication failure

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Success/Authenticator Response

   (Authenticator Response verification fails, peer disconnects)

9.1.3.  Failed authentication with no retry allowed

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Failure (E=691 R=0)

   (Authenticator disconnects)

9.1.4.  Successful authentication after retry

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Failure (E=691 R=1), disable short timeout
       Response (++ID) to challenge in failure message ->
                         <- Success/Authenticator Response

   (Authenticator Response verification succeeds, call continues)

9.1.5.  Failed hack attack with 3 attempts allowed

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Failure (E=691 R=1), disable short timeout
       Response (++ID) to challenge in Failure message ->
                         <- Failure (E=691 R=1), disable short timeout
       Response (++ID) to challenge in Failure message ->
                         <- Failure (E=691 R=0)








Zorn                         Informational                     [Page 15]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


9.1.6.  Successful authentication with password change

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Failure (E=648 R=0 V=3), disable short
   timeout
       ChangePassword (++ID) to challenge in Failure message ->
                         <- Success/Authenticator Response

   (Authenticator Response verification succeeds, call continues)

9.1.7.  Successful authentication with retry and password change

                         <- Authenticator Challenge
       Peer Response/Challenge ->
                         <- Failure (E=691 R=1), disable short timeout
       Response (++ID) to first challenge+23 ->
                         <- Failure (E=648 R=0 V=2), disable short
   timeout
       ChangePassword (++ID) to first challenge+23 ->
                         <- Success/Authenticator Response

   (Authenticator Response verification succeeds, call continues)

9.2.  Hash Example

   Intermediate values for user name "User" and password "clientPass".
   All numeric values are hexadecimal.

0-to-256-char UserName:
55 73 65 72

0-to-256-unicode-char Password:
63 00 6C 00 69 00 65 00 6E 00 74 00 50 00 61 00 73 00 73 00

16-octet AuthenticatorChallenge:
5B 5D 7C 7D 7B 3F 2F 3E 3C 2C 60 21 32 26 26 28

16-octet PeerChallenge:
21 40 23 24 25 5E 26 2A 28 29 5F 2B 3A 33 7C 7E

8-octet Challenge:
D0 2E 43 86 BC E9 12 26

16-octet PasswordHash:
44 EB BA 8D 53 12 B8 D6 11 47 44 11 F5 69 89 AE





Zorn                         Informational                     [Page 16]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


24 octet NT-Response:
82 30 9E CD 8D 70 8B 5E A0 8F AA 39 81 CD 83 54 42 33 11 4A 3D 85 D6 DF

16-octet PasswordHashHash:
41 C0 0C 58 4B D2 D9 1C 40 17 A2 A1 2F A5 9F 3F

42-octet AuthenticatorResponse:
"S=407A5589115FD0D6209F510FE9C04566932CDA56"

9.3.  Example of DES Key Generation

   DES uses 56-bit keys, expanded to 64 bits by the insertion of parity
   bits.  After the parity of the key has been fixed, every eighth bit
   is a parity bit and the number of bits that are set (1) in each octet
   is odd; i.e., odd parity.  Note that many DES engines do not check
   parity, however, simply stripping the parity bits.  The following
   example illustrates the values resulting from the use of the password
   "MyPw" to generate a pair of DES keys (e.g., for use in the
   NtPasswordHashEncryptedWithBlock() described in section 8.13).

   0-to-256-unicode-char Password:
   4D 79 50 77

   16-octet PasswordHash:
   FC 15 6A F7 ED CD 6C 0E DD E3 33 7D 42 7F 4E AC

   First "raw" DES key (initial 7 octets of password hash):
   FC 15 6A F7 ED CD 6C

   First parity-corrected DES key (eight octets):
   FD 0B 5B 5E 7F 6E 34 D9

   Second "raw" DES key (second 7 octets of password hash)
   0E DD E3 33 7D 42 7F

   Second parity-corrected DES key (eight octets):
   0E 6E 79 67 37 EA 08 FE

10.  Security Considerations

   As an implementation detail, the authenticator SHOULD limit the
   number of password retries allowed to make brute-force password
   guessing attacks more difficult.








Zorn                         Informational                     [Page 17]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


11.  References

   [1]  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
        1661, July 1994.

   [2]  Simpson, W., "PPP Challenge Handshake Authentication Protocol
        (CHAP)", RFC 1994, August 1996.

   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [4]  "Data Encryption Standard (DES)", Federal Information Processing
        Standard Publication 46-2, National Institute of Standards and
        Technology, December 1993.

   [5]  Rivest, R., "MD4 Message Digest Algorithm", RFC 1320, April
        1992.

   [6]  RC4 is a proprietary encryption algorithm available under
        license from RSA Data Security Inc.  For licensing information,
        contact:

             RSA Data Security, Inc.
             100 Marine Parkway
             Redwood City, CA 94065-1031

   [7]  Eastlake, D., Crocker, S. and J. Schiller, "Randomness
        Recommendations for Security", RFC 1750, December 1994.

   [8]  "The Unicode Standard, Version 2.0", The Unicode Consortium,
        Addison-Wesley, 1996. ISBN 0-201-48345-9.

   [9]  Zorn, G. and Cobb, S., "Microsoft PPP CHAP Extensions", RFC
        2433, October 1998.

   [10] "DES Modes of Operation", Federal Information Processing
        Standards Publication 81, National Institute of Standards and
        Technology, December 1980.

   [11] "Secure Hash Standard", Federal Information Processing Standards
        Publication 180-1, National Institute of Standards and
        Technology, April 1995.

   [12] Zorn, G., "PPP LCP Internationalization Configuration Option",
        RFC 2484, January 1999.






Zorn                         Informational                     [Page 18]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


12.  Acknowledgements

   Thanks (in no particular order) to Bruce Johnson, Tony Bell, Paul
   Leach, Terence Spies, Dan Simon, Narendra Gidwani, Gurdeep Singh
   Pall, Jody Terrill, Brad Robel-Forrest, and Joe Davies for useful
   suggestions and feedback.

13.  Author's Address

   Questions about this memo can also be directed to:

   Glen Zorn
   Microsoft Corporation
   One Microsoft Way
   Redmond, Washington 98052

   Phone: +1 425 703 1559
   Fax:   +1 425 936 7329
   EMail: gwz@acm.org
































Zorn                         Informational                     [Page 19]

RFC 2759                  Microsoft MS-CHAP-V2              January 2000


14.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Zorn                         Informational                     [Page 20]